Template function declarations

I am attempting to create a template function as follows:

template <typename T> DWORD GetRegistryDword (T key)
{
     tstring subKey(key);

        //snip

     return retVal;
}

The function works perfectly, but when I try to place it in a separate source file, I get a LNK1120, unresolved external.  I have created the files as follows:

registry.h:
template <typename T> DWORD GetRegistryDword (T key);

registry.cpp:
#include <windows.h>
#include <string>
#include "registry.h"
(see above implementation)

main.cpp:

#include <windows.h>
#include <registry.h>

int main()
{
    DWORD dwReturn = GetRegistryDword("HKEY_LOCAL_MACHINE\\...\\blah");
}

I have noticed that when I move my implementation into registry.h I no longer get the unresolved external in main.cpp, but I don't really want to place the entire implementation for all of my template functions into header files.  Is there any way around this?